City of Boise composting process.
“Good compost smells really rich and earthy with a slightly sweet smell, like a fig newton!”
This is Sydney Bennett, materials management environmental analyst for the city of Boise, raving about the city’s 2-year-old composting program. The program started in June 2017.
“Over the past two years, the Boise compost project collected 54,000 tons of material to process and get it back to Boise residents. On average that is 60 pounds per house per month over the lifetime of the project. That is 1,472 pounds per household over two years,” Bennett said.
Composting is not just good for the environment. It also saves the city money at the landfill in terms of land usage and money for management and transportation.
“From 2016, before we started the composting program, to 2018, one year in, we saw a 26% decrease in pounds of garbage per household per month in Boise,” Bennett said. “From the city’s perspective it is an overwhelming success, with a 97% participation rate of Boise residents.”
Despite the success, the city says residents are still putting noncompostable items like plastic, rocks and toys in the compost bin. These contaminants can cause issues in the composting process because they require additional screening to remove.
Newcomers and veterans of the Boise composting program should be aware of a few reminders about what Boise can and cannot compost. Natalie Monro, public works communications coordinator; Colin Hickman, public works communications manager; and Bennett helped with reminders and information about the composting process.
Residents can place up to 10 paper bags of lawn waste and large items such as Christmas trees next to their bins for pickup as long as they are smaller than 4 feet.
Dairy and meat products cannot be composted. Boise does not have the facilities to compost these materials.
Do not put plastic bags in the compost bin. During the composting process plastic bags become plastic confetti that can land in the finished compost pile and contaminate the surrounding natural area. Boise’s composting process is also not long enough to break down plastic compostable bags like kitchen composting bags. If you need to bag your compost, use a paper bag, not plastic.
Rocks are not compostable and clog the composting system.
Screen your lawn waste for dog toys. Tennis balls do not compost and your dog will miss them.
So how does composting work?
Composting is an easy, sustainable way to use green waste to create rich, organic compost to boost garden productivity, but there can be misconceptions about the process.
Here in Boise, trucks collect residential composting on the same day as trash pickup. These trucks drive the lawn clippings and kitchen waste to Twenty Mile South Farm, south of Boise. Composting trucks are weighed on their way in and out of the facility to track the number of pounds collected from Boise residents. Trucks dump the organic material into rows to manually remove obvious contaminants like plastic bags and large rocks. The organic material is then ground to an even size to increase the composting speed.
The organic material is placed into 100-foot-long windrows, or long piles that are 6 to 8 feet tall. There can be up to 20 windrows at the Boise composting facility. Heat and oxygen drive the composting process. These long and tall rows reach temperatures up to 150 degrees during the active composting stage, killing most pathogens and seeds. Windrow turners aerate the piles, bringing oxygen to the composting material and accelerating the process. At temperatures of 140 to 150 degrees, the windrow pile can reduce 40% in volume over 70 to 90 days, becoming dense and dark compost material. The City of Boise uses several metrics to ensure the compost meets the U.S. Composting Council’s standards for use in fruit and vegetable gardens, including testing for carbon, nitrogen, seed presence and pesticide presence.
Once the compost material passes the tests and is screened for any additional woody debris or plastics, it is ready for residents. Boise residents who participate in the composting program can collect up to 2 cubic yards of finished compost each year from one of two locations: the Idaho Botanical Garden or the new Joplin Road compost site in West Boise. These locations are self-serve, so bring your own buckets and shovels.
Why use compost?
“Composting is putting organic materials together, then those things with heat and oxygen decompose, and they will eradicate the pathogens and diseases and will leave things that are readily available for plants,” said Trent Cummins, lead of operations at Cowgirl Compost, a full-service dairy compost company based in Idaho.
As compost matures, it breaks large organic material into more basic material which makes nutrients like carbon, nitrogen, and potassium more accessible for plants to use. Compost also slowly releases these nutrients over two to four years, making it a more efficient garden amendment than fertilizer.
“Soils in Idaho, there’s a lot of minerals in the soil that are present but not readily available for plants,” Cummins said. “For example, Idaho has a lot of calcium in the soil but it is not readily available because it is locked up in another structure, like limestone. But because it has been composted then it is readily available for plants to use.”
Kitchen scraps, lawn waste and manure are great compost ingredients with lots of important nutrients and minerals. Good organic material going into Boise’s composting program means good compost coming out for Boise residents to use to grow healthy fruits and vegetables.
“Compost is not all the same thing, quality compost depends on what you are putting in there,” Cummins said.
Rachel Hager is writing for the Idaho Statesman this summer on a fellowship through the American Association for the Advancement of Science. She is a master’s student in ecology at Utah State University and earned a bachelor’s degree in biology at Bryn Mawr College.